There are number of different potential handoffs that can occur for a MS. These include, as non-limiting examples, inter-PDSN (Packet Data Service Node) handoffs, inter-BS (Base Station) hard handoffs, inter-BS soft handoffs, and inter-PCF (Packet Control Function) hard handoffs. In each of these different types of handoffs a problem that arises is related to preserving the context of the connection with the MS during the transfer. This invention is directed towards solving the context transfer problems that arise in the inter-BS and inter-PCF handoff cases. Commonly assigned U.S. patent application Ser. No. 10/878,452, filed on even date herewith and entitled “Method and Apparatus Providing Context Transfer for Inter-PDSN Handoffs in a Wireless Communication System”, by Jianhao Michael Yang, Sarvesh Asthana and Rajeev Koodli, is directed towards solving the context transfer problems that arise in the inter-PDSN handoff scenario, and may thus be considered a related application to this patent application, and is incorporated by reference herein in its entirety.
The CDMA 2000 3GPP2 specification A.S0013 describes in detail the call flow involved in performing an inter-BS hard handoff and an inter-PCF hard handoff. As quality of service (QoS) issues are becoming more important to network operators and also to users it is expected that handoffs should not only solve the connectivity problem, but also provide the same QoS after a handoff. The call flow that is specified in the CDMA 2000 3GPP2 specification A.S0013 touches upon the QoS aspects involved in the hard handoff, but does not give a complete solution to maintaining the same QoS after the handoff. For example, before the hard handoff the serving or anchor BS, as well as the serving or anchor PCF, may maintain some state information to provide a negotiated level of QoS to the MS. However, this state information needs to be transferred over to the target BS, and to the target PCF, in order to provide a seamless handover in terms of MS QoS expectations
Also, there is a period of time when the MS is switching from one physical channel to the other physical channel during a handoff that there is no connectivity between the MS and the network. This raises the possibility that data packets being sent to and from the MS can become lost.
In addition to the hard inter-BS and inter PCF handoffs, there are applications in the mobile network that require mobility management to maintain session continuity. Mobility management at the link layer is achieved though a soft handoff mechanism. The use of the soft handoff obviates the need to re-establish a session whenever the MS moves from one BS to another BS.
The current CDMA standard supports multiple service instances for a given MS. Relatedly, the soft handoff for multiple service instances requires careful consideration as to providing a seamless transfer of the context or QoS parameters from the source BS to the target BS for each MS service instance. The goals of such mobility management include eliminating service interruptions, reducing packet loss and delay time, and hence increasing the QoS.
A generic context transfer protocol has been previously proposed. However, at least two issues remain unaddressed in the existing context transfer mechanism.
A first issue is related to the contexts for real time applications such as VoIP (Voice over Internet Protocol), where the time sensitivity and accuracy of the transferred context is critical.
A second issue is related to link layer contexts versus IP layer contexts or application contexts. The link layer context is typically technology specific, and is normally coupled together with the handoff mechanism for that wireless technology, whereas in general the IP layer contexts or application contexts are more generic, and are less reliant on the underlying wireless technology.
For the case of CDMA wireless technology, when the MS performs an inter-BS soft handoff there are two types of contexts that can be transferred:    1. Static contexts such as SR_ID, service option, radio configuration, etc.; and    2. Dynamic contexts, such as link layer assisted header compression information. For example, the HRL (Header Reduction Lower) state information for LLA-ROHC (Link Layer Assisted-Robust Header Compression).
The dynamic type of context is time sensitive, implying that this type of context should be kept updated in order to ensure accuracy. Prior to this invention, there was no adequate context transfer mechanism for CDMA inter-BS soft handoffs.
The following standards are related to this invention: 3GPP2 TSG X.P0011.3: Wireless IP Network Standard: Packet Data Mobility and Resource Management; 3GPP2 TSG X.P0011.2: Wireless IP Network Standard: Simple IP and Mobile IP Access Services; 3GPP2 TSG A.S0013-A v2.0.1: 3GPP2 IOP for CDMA2000 Access network Interface; “Fast Handovers for Mobile IPv6”, IETF [mobile-ip] Working Group draft, Rajeev Koodli (Ed.), Jan. 30, 2004; “Fast Handovers and Context Transfers in Mobile Networks”, Rajeev Koodli and Charles E. Perkins, Computer Communication Review, apublication of ACM SIGCOMM, volume 31, number 5, October 2001. ISSN # 0146-4833; and RFC3220: IP Mobility Support for IPv4, C. Perkins (Ed.) January 2002.
As was the case of the inter-BS and inter-PCF hard handoffs discussed above, the CDMA 2000 3GPP2 specification A.S0013 details the call flow involved in performing inter-BS soft handoffs. As in the hard handoff case, the serving BS before the handoff may be maintaining state information to provide the negotiated QoS to the MS. During the soft handoff the state information needs to be transferred to the target BS in order to provide the seamless handover in terms of quality of service expectations.
Also, for those services involving multiple service instances, such as VoIP, there are different types of state information that should be handled differently depending on the nature of how the contexts are used.
It should thus be apparent that there is a need to provide improved techniques for performing inter-BS hard and soft handoffs, as well as inter-PCF hard handoffs. Prior to this invention, these needs were not adequately addressed or fulfilled.